With Vista, the install DVD should contain all versions - your product key then determines which one will be installed.
The following download links are from Digital River. They still work now, but I wouldn't be surprised if they go away in the next month (Vista hits end of life in less than 30 days, on 04/10/2012).
Digital River download links for Vista Ultimate SP1 x86:
Digital River download links for Vista Ultimate SP1 x64:
Guide to create Vista install DVD with vLite
(use X14-635452.EXE in place of the reference to X14-49121.EXE in the guide for the 32 bit install CD).
Note: Guide is for creation of 64-bit Vista install DVD, but also works for X86/32-bit install DVD creation if you skip the ETFSBOOT.COM step
Hope this helps.